A double-headed swash plate type compressor applied to an automobile air conditioning system, for example, has a drive shaft, a pair of cylinder blocks supporting the drive shaft for rotation, and a swash plate fixedly supported on the drive shaft for rotation together with the drive shaft in a swash plate chamber formed in a region including the boundary between the pair of cylinder blocks. A plurality of cylinder bores are formed so as to extend in both the cylinder blocks and are arranged around the drive shaft. Double-headed pistons are fitted for axial movement in the cylinder bores, respectively. Each piston is operatively engaged with the swash plate by shoes. The rotary motion of the swash plate is converted into the linear motion of the pistons for the suction, compression and discharge of a refrigerant gas.
A single-headed swash plate type compressor has a cylinder block and a housing closing the inner end of the cylinder block and having a swash plate chamber or a crank chamber. A swash plate is mounted on a drive shaft in the swash plate chamber and is linked to pistons by shoes. In a variable-displacement swash plate compressor, a swash plate is linked to single-headed pistons fitted in a plurality of cylinder bores by shoes, and is mounted on a drive shaft so as to wobble on a supporting point. The inclination of the swash plate is changed according to pressure in the crank chamber so that gas pressures acting on the opposite ends of the single-headed piston balance each other. Consequently, the stroke of the single-headed piston is adjusted to control the displacement of the compressor.
A significant demand for weight reduction in those swash plate type compressors has progressively increased in order to apply the swash plate type compressors to automobile air conditioning systems, and most of the swash plates and the pistons, as well as the cylinder blocks, of those swash plate type compressors are made of aluminum alloys in lightweight constructions. Therefore, abrasion-resistant and seizing-preventive measures have been examined for protecting surfaces exposed to severe, high-speed abrasive action for a long time, such as the surfaces of the swash plate in sliding contact with the shoes, and the sliding contact surface of the piston in sliding contact with the surface of the bore. Such measures include the formation of a fluorocarbon resin film on the sliding contact surface of the piston and the formation of a film of a solid lubricant on the sliding contact surface of the swash plate.
However, the double-headed piston is provided with a recess extending across the periphery of the swash plate, and interfering surfaces formed in the recess to restrain the piston from rotation come into impulsive contact with the outer circumference of the swash plate to restrain the piston from rotation by a rotation moment acting on the piston. The single-headed piston is provided with a rotation-preventive interfering surface in its base end part, and the interfering surface comes into impulsive contact with the inner surface of the housing to restrain the piston from rotation. Accordingly, it is possible, under a substantially nonlubricated state which occurs at the start of the compressor, that seizing occurs at the interfering surface of the piston and the outer circumference of the swash plate, and attempts have been made to form a lubricating film over the interfering surface of the piston and the outer circumference of the swash plate. Nevertheless, the yield of a coating material used in, for example, a spray coating process for coating the pistons and the swash plate with a lubricating film is extremely low. Furthermore, the spherical surfaces of the pistons must be masked in the spray coating process and the spray coating process is hardly satisfactory in working efficiency.